1. Field of the Invention
The present invention relates to luminescent material for use as military tracer rounds and more particularly, to such materials whose photoluminescence is excited by the energy emitted by military propellants and are thereby observable at night, with the aid of conventional night vision devices.
2. Related Art
Historically, gunners relied on observing the impact of their bullets (i.e. projectiles) in order to adjust their aim—which is not effective, as often the impact point is not visible. As a solution to this problem, in about 1915 tracer ammunition (also referred to as pyrotechnic tracer, standard tracer, standard pyrotechnic tracer, and/or M62 Tracer) was introduced—ammunition containing a pyrotechnic composition that burned very brightly—making the projectile visible to the naked eye. A disadvantage of such brightly burning pyrotechnic is that the enemy can easily trace back the stream of tracer ammunition to disclose the gunner's position. To help remediate this problem, subdued tracers have a built in delay—which causes them to burn brightly after at least 100 yards—such that it isn't easy to establish the position of the gunner. But, such a delay is only partially effective—so, dim tracers were introduced, wherein the tracer can only be viewed with the aid of night vision equipment—allowing the gunner to better observe his fire and “walk” it to the desired location in low light or night conditions.
Most modern military forces use projectiles containing energetic tracer materials based on technology developed in the early 1900s. Such tracer materials are generally pyrotechnic compositions, which are composed of mixtures of a fuel reactant and an oxidizer reactant—such that no external sourced oxygen is required to sustain the reaction. The subject incendiary reaction generates light through a self-sustaining, non-detonative, exothermic chemical reaction, similar to that used in a road flare. Despite various technological advancements that have been made in the years since such pyrotechnic tracers were introduced, such pyrotechnic energetic type tracers still have significant shortcomings. These shortcomings include—(1) the exothermic incendiary nature of energetic tracer materials makes them a fire hazard—especially in wooded or grass covered training areas—and can present significant undesirable consequence in battle; (2) the tracers lose mass in flight as the pyrotechnic reaction progresses, creating an inherent inaccuracy and lack of precision; (3) the particular pyrotechnic materials used for energetic tracers create environmental and hazardous material problems; (4) the energetic tracer, using incendiary fuels and oxidizers are difficult to manufacture; and, finally, (5) pyrotechnic energetic tracers are bi-directional, i.e. meaning they can be seen by the shooter as well as the enemy.
Conventional, standard energetic tracer projectiles typically hold the pyrotechnic material in a hollow or cavity located within their base or rear section, as shown in FIG. 1. Conventional dim tracers are similar in design to such standard pyrotechnic daylight/night tracers; except, for a different pyrotechnic mix. In either case, the pyrotechnic material is ignited by the burning of the energetic propellant within the cartridge that houses the projectile and the pyrotechnic burns brightly during its flight to target.
The usual practice is to load cartridges containing energetic tracers, i.e. tracer rounds or bullets, into an ammunition belt at a ratio of one tracer bullet per every four non-tracer rounds, in ground-based guns, and one tracer per every four or nine non-tracer rounds in aircraft mounted guns. Unfortunately, energetic tracers can never be a totally reliable indicator of a gunner's aim, because the energetic tracer projectiles have different aerodynamic properties and weights when compared to standard rounds/projectiles that are being fired with the energetic tracer. This difference is primarily due to the fact that the mass of the energetic tracer changes as the pyrotechnic material burns, and is ejected out of the cavity in the back of the projectile during flight (pyrotechnic tracers typically leave behind a narrow cloud of burning material that can be up to about a meter long), versus the unchanging mass of a non-tracer projectile. By design, tracer and non-tracer rounds match their relative trajectories at about 600 yards.
Because the material used to manufacture energetic tracers is pyrotechnic, energetic tracer ammunition must be produced in a production line separate from any standard ammunition production line, due to safety concerns. Further, in order to accommodate the tracer material, the length of an energetic tracer bullet is typically longer than a standard bullet of the same caliber. The increased length also adds to the complexity of manufacture because the tracer bullet takes up additional space in the cartridge that would otherwise be used for the propellant in a non-tracer round.
There have been attempts to produce tracers without the shortcomings mentioned above. For example, U.S. Patent Application Publication No. 2004/0099173 teaches the use of a light emitting diode (LED) and capacitor, in-place of a pyrotechnic material, in an attempt to decrease tracer visibility. Likewise, U.S. Patent Application Publication No. 2005/0034627 teaches the use of an electronic light source in lieu of the use of a pyrotechnic material. However, such attempts still result in a tracer bullet with a mass substantially different than the normal bullet.
Furthermore, U.S. Pat. Nos. 6,497,181 and 6,990,905 teach the use of materials in tracer ammunition whereby two chemicals are mixed together to provide a chemical reaction subsequent to firing or launching of the bullet, thereby creating visible light. This is known as a chemiluminescent material. This type of tracer ammunition provides a trace of the path of the projectile and also serves as a marker; whereby, the projectile breaks apart upon impact, scattering the chemiluminescent material. However, the use of chemiluminescent materials in tracer ammunition requires a chemical reaction, wherein at least two chemiluminescent materials need to react to form at least one new compound. Such tracer rounds require an added manufacturing expense because of the need to separate the individual chemicals prior to firing. This separation of chemicals may also take up space in the bullet, making it either less massive, or making the bullet longer to provide for the chemical chambers. Further, the separation of chemicals will also make the bullet more prone to damage during handling. In addition, after firing, the two chemicals must adequately mix in order to result in the desired luminescence. Also suitable environmental conditions may be needed to allow the chemical reaction to occur. Furthermore, the chemiluminescent tracers can only be seen in flight by way of a transparent window in the bullet, which has practical constraints due to the material limitations and installation of the window.
Another alternative tracer is disclosed in U.S. Pat. No. 8,402,896, which details photoluminescent tracer materials. Unfortunately, the particular photoluminescent materials disclosed have been proven to be ineffective, as not bright enough for use with the currently available night vision equipment at the required minimum distance of about 400 meters.
Consequently, there is a need for new low light or night condition tracer projectiles, usable with night vision equipment, capable of overcoming the shortcomings of the current alternatives as detailed above.